This application claims priority of Korea patent Application No. 10-2000-0055108, filed on Sep. 20, 2000.
(a) Field of the Invention
The present invention relates to a method for controlling a glow plug, and more particularly, to a method for controlling power supplied to the glow plug by dividing an engine starting step into a cranking step and an idling step, and operating the glow plug even after successfully entering into a running state in the case of entering into an abnormal engine state based on an amount of injected fuel, an engine speed and a coolant temperature, and thereby controlling the glow plug from before the engine starts through after it is running.
(b) Description of the Related Art
A conventional diesel engine is a compression-ignition type engine, which ignites fuel by injecting it into a combustion chamber heated to a high temperature by compressing air in a cylinder. Ignition of the conventional diesel engine may be unstable when the engine is at a low temperature in an early state of engine starting in which the engine is cold, because compression heat is not sufficient.
To enhance startability of a diesel engine when it is cold, a glow plug is installed in each cylinder and operated before starting the engine in order to heat air around the glow plug.
A conventional method for controlling a glow plug by prior art is simply to heat the glow plug for a given period of time according to coolant temperature.
According to the prior art, there is a problem of high power consumption. For example, the glow plug heating is continued in an unnecessary situation because the heating time is unchangeably determined by data acquired during starting. Therefore the battery may be frequently discharged because of high power consumption and the engine can be stalled in the process of starting because too much electrical power stored in the battery can be consumed by heating the glow plug.
Therefore, the present invention has been made in an effort to solve the above problem. An object of the present invention is to provide a method for controlling power supplied to a glow plug by dividing an engine starting step into a cranking step and an idling step, and operating the glow plug in the case of entering into an abnormal engine state even after successfully entering into a running state, based on an amount of injected fuel, engine speed and coolant temperature, and thereby controlling the glow plug from before the engine starts through after it is running, and stopping the process of control for a short time when a battery voltage is low.
Generally, a starter motor is rotated by operating a start switch, and thereby starting begins. The process of engine starting is made up of a cranking step in which the engine starts to rotate and an idling step in which the engine idles immediately after the engine is started.
Therefore, to achieve the above object, the method for controlling the glow plug according to the present invention controls power supplied to the glow plug by dividing the engine starting step into the cranking step and the idling step. Furthermore, the glow plug is operated even after the engine successfully starts, when the engine is in an abnormal state based on an amount of injected fuel, engine speed and coolant temperature.
A preheating system using a method for controlling a glow plug according to the present invention includes the glow plug being fixed on one side of a cylinder head, a battery supplying power to the glow plug, a control unit controlling power supply from the battery to the glow plug through a relay, a coolant temperature sensor measuring the temperature of the coolant, a battery voltage sensor measuring the voltage of the battery, and means for measuring an amount of injected fuel.
A method for controlling the glow plug of the present invention applies power to the glow plug until a power supply time exceeds a predetermined initial preheating time, or the engine is cranked, at which time the power supply to the glow plug is maintained until the power supply time exceeds a predetermined main preheating time, the engine enters into the idling state, or the coolant temperature is higher than a predetermined target value, and then the power supply to the glow plug is cut off.
The initial preheating time and the main preheating time are determined by tables that use the battery voltage and the coolant temperature as variables.
When the engine speed is greater than a predetermined speed for a predetermined time, the engine is determined to be cranking. When the engine speed reaches a predetermined speed, the engine is determined to be idling.
As the engine starts idling, the amount of injected fuel and the engine speed are measured. When the amount of injected fuel is greater than a predetermined fuel injection reference amount, or the engine speed is greater than a predetermined reference speed, the glow plug is preheated until the amount of fuel being injected and the engine speed become respectively lower than the fuel injection reference amount and the reference speed.
After engine starting is complete, when the coolant temperature is lower than a determined critical temperature, or the amount of injected fuel is less than a determined critical amount of injected fuel, or the engine speed is lower than a determined critical speed, the glow plug is again preheated until the coolant temperature, the amount of injected fuel and the engine speed are respectively greater than the critical values.
In each control step, when the battery voltage being measured is lower than a predetermined critical voltage, the power supply to the glow plug and the execution of the detailed steps are stopped. The power supply to the glow plug and the execution of the detailed steps remain stopped until the battery voltage is higher than the critical voltage, and then the power supply to the glow plug and the execution of the detailed steps are resumed.